American Journal of Epidemiology Advance Access published online on September 12, 2007
American Journal of Epidemiology, doi:10.1093/aje/kwm202
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Original Contribution |
Objectively Assessed Associations between Physical Activity and Body Composition in Middle-School Girls
The Trial of Activity for Adolescent Girls
1 Department of Nutrition, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC
2 Department of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC
3 Division of Epidemiology, School of Public Health, Ohio State University, Columbus, OH
4 Department of Health Promotion and Behavioral Sciences, Graduate School of Public Health, San Diego State University, San Diego, CA
5 Department of Physiology, College of Medicine, University of Arizona, Tucson, AZ
6 Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis, MN
7 Department of Exercise Science, Arnold School of Public Health, University of South Carolina, Columbia, SC
8 Division of Prevention and Population Sciences, National Heart, Lung, and Blood Institute, Bethesda, MD
9 Center for Human Nutrition, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD
10 Department of Biostatistics, School of Public Health and Tropical Medicine, Tulane University, New Orleans, LA
11 Department of Kinesiology, College of Health and Human Performance, University of Maryland, College Park, MD
Correspondence to Dr. June Stevens, CB 7400, Department of Nutrition, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 (e-mail: June_stevens{at}unc.edu).
Received for publication March 26, 2007. Accepted for publication June 12, 2007.
Declining levels of physical activity probably contribute to the increasing prevalence of overweight in US youth. In this study, the authors examined cross-sectional and longitudinal associations between physical activity and body composition in sixth- and eighth-grade girls. In 2003, girls were recruited from six US states as part of the Trial of Activity for Adolescent Girls. Physical activity was measured using 6 days of accelerometry, and percentage of body fat was calculated using an age- and ethnicity-specific prediction equation. Sixth-grade girls with an average of 12.8 minutes of moderate-to-vigorous physical activity (MVPA) per day (15th percentile) were 2.3 times (95% confidence interval: 1.52, 3.44) more likely to be overweight than girls with 34.7 minutes of MVPA per day (85th percentile), and their percent body fat was 2.64 percentage points greater (95% confidence interval: 1.79, 3.50). Longitudinal analyses showed that percent body fat increased 0.28 percentage points less in girls with a 6.2-minute increase in MVPA than in girls with a 4.5-minute decrease (85th and 15th percentiles of change). Associations between MVPA in sixth grade and incidence of overweight in eighth grade were not detected. More population-based research using objective physical activity and body composition measurements is needed to make evidence-based physical activity recommendations for US youth.
adipose tissue; adolescent; anthropometry; body composition; body mass index; exercise; growth; longitudinal studies
Abbreviations: BMI, body mass index; MET, metabolic equivalent; MVPA, moderate-to-vigorous physical activity; TAAG, Trial of Activity for Adolescent Girls